Ultra-fast green synthesis of a defective TiO₂ photocatalyst towards hydrogen production

An ultra-fast green synthesis of defective titanium dioxide (TiO₂) photocatalysts was conducted by the microwave-assisted method using l-ascorbic acid (l-As) as a reducing agent. Effect of l-As concentrations on the chemical-, optical- and photoelectrochemical properties as well as the photocatalytic performance towards the hydrogen (H₂) production was explored. The obtained TiO₂ nanoparticles (NPs) illustrated the brown fine powders with different brownness levels depending on the concentrations of l-As. A high l-As concentration provided a high brownness of TiO₂ NPs with a high generation of Ti³⁺ defects and oxygen vacancies (O_v), which can extend the light absorption towards the visible and near-infrared regions, suppress the recombination rate of electron-hole pairs, promote the photocurrent response and minimize the interface charge transfer resistance. An appropriate quantity of generated defects and good porous properties played a crucial role in photocatalytic H₂ production. Under fluorescence illumination, the sample synthesized with a TiO₂ and l-As weight ratio of 1 : 0.25 (PAs0.25) exhibited the highest H₂ production rate (∼162 μmol g^-1 h^-1 in the presence of 1 wt% Au co-catalyst) with a slight drop (∼8.2%) after the 5th use (15 h). The synthesis method proposed in this work provides a new insight to an ultra-fast synthesis of defective TiO₂ NPs using an eco-friendly chemical precursor under non-severe conditions.